1. Field of Invention
The present invention relates to a multi-color rotary printing machine                in which one printing plate support each is assigned to the colors to be transferred onto the print substrate, whereby said printing plate support supports a printing plate and        can be attached to a mandrel or a cylinder of a rotary printing machine in order to transfer the print image onto the print substrate,        whereby the rotary printing machine has register devices that determine the position of the printing plates with respect to one another.        
2. Description of the Prior Art
Machines of such type are designed, for example, as flexographic printing machines and gravure printing machines. The term “printing plate support” refers to all possible cylinders, sleeves, or even flexible mats that support a printing plate. Thus, for example, a cylinder that supports a printing plate and is supported using bearing pins and/or bearing points is used conventionally in gravure printing. However, in recent times the so-called sleeves that are drawn up over a cylinder are also used in gravure printing just as in case of flexographic printing. Many different colors are used particularly in package printing. As a result, the high demands made on register accuracy play an important role in this context. However, register accuracy also plays an important role in other areas and in the application of other print processes. The still unpublished patent application having the file number 102 54 836. 6-27 and that has also been submitted to the German Patent and Trademark Office addresses this issue of register processes in detail.
In the literature relevant to this subject, no mention is usually made of the manner in which the positions of the printing plate supports with respect to one another are determined before and at the time of the start of the print process. Said positions are determined, for example, in flexographic printing machines of prior art by an alignment of the printing plate—usually an alignment of a printing sleeve to a pin protruding in the radial direction over the peripheral surface of the print cylinder.
The printing sleeve has a recess into which the pin fits with relative accuracy. It is a laborious and time-consuming process for the machine operator to align the printing sleeve correctly. This process is often referred to as pre-register control.
In addition to that, the clearance between the pin and the recess results in inaccuracies during the register control.
This clearance strongly increases in direct proportion to the service life particularly of printing plate supports of flexographic printing that are manufactured from plastic and are often replaced. Register errors can often occur and/or multiply even during the ongoing operation if printing plates, while in operation, shift on the mandrels or the cylinders on which they are seated.
A more accurate pre-register control of the sleeve that could reduce the said disadvantages also forms the subject matter of U.S. Pat. No. 5,551,339. Said document illustrates a printing machine that is provided with sensor devices which observe the peripheral surface of the printing sleeves. Information carriers are located on the peripheral surface of the printing sleeves. The position of the information carriers is recorded after the sleeves are inserted into the machine and before the start of the actual printing operation. After the angle position of the sleeve on the mandrel on which it is located is determined, the torque-proof connection between the mandrel and the sleeve is broken, the sleeve is grasped by a frame-fixed gripping devices and prevented from bringing about a rotation of the mandrel. Subsequently, the sleeve being stationary, the mandrel is rotated in such a manner that a relative target position between the sleeve and the mandrel sets in. U.S. Pat. No. 6,314,883 also describes a process of pre-register control in which an information carrier attached to the sleeve and a sensor are specified for recording the position of said sleeve.